Torsion beam accelerometer with slotted tilt plate

Abstract

A capacitive-type torsion beam accelerometer sensor element exhibiting improved stability contains slots in the heavy side of the rotatable sensing element which serve to alter the geometry of the heavy side capacitor such that the electrical geometry substantially coincides with the physical geometry of the substrate's fixed conductive plate in the presence of charge spreading. The slots also permit ingress and egress of air, thus extending the frequency response.

What is claimed is: 
     
       1. A torsion beam accelerometer sense element, comprising: a substantially planar substrate;   a sensing member positioned above and parallel to said substrate and rotatable about a flexure axis, the portion of said sensing member on one side of said flexure axis being larger in area than the portion of said sensing member on the other side of said flexure axis;   first and second conductive surfaces arrayed substantially symmetrically on said substrate about said flexure axis, said second conductive surface coacting with said larger side of said sensing member to define a heavy side deflection capacitor, said first conductive surface coacting with said other side of said sensing member to define a light side deflection capacitor;   isolation means effective to limit the electrical geometry of said heavy side capacitor to substantially the physical geometry of said first conductive surface in at least one dimension;   wherein said sensing member rotates about said flexure axis responsive to acceleration normal to the surface of said substrate, and wherein the capacitance of said heavy side and light side capacitors change in response to said rotation.   
     
     
       2. The sense element of claim 1 wherein said sensing member comprises a planar semiconductive body having an opening along said flexure axis, said opening having therein a pedestal fixedly mounted to said substrate and a pair of opposed torsion arms connecting said pedestal to said planar semiconductive body, said torsion arms defining said flexure axis. 
     
     
       3. The sense element of claim 2 wherein said substrate is a dielectric substrate and wherein said first and second conductive surfaces comprise metallized portions of the surface of said substrate. 
     
     
       4. The sense element of claim 1 wherein said isolation means comprises a plurality of slots in said larger side of said sensing member, said slots defining a portion of said larger side of said sensing member substantially corresponding with said second conductive surface. 
     
     
       5. The sense element of claim 2 wherein said isolation means comprises a plurality of slots in said larger side of said sensing member, said slots defining a portion of said larger side of said sensing member substantially corresponding with said second conductive surface. 
     
     
       6. The sensor element of claim 3 wherein said isolation means comprises a plurality of slots in said larger side of said sensing member, said slots defining a portion of said larger side of said sensing member substantially corresponding with said second conductive surface. 
     
     
       7. The sense element of claim 2 wherein said planar semiconductive body, said pedestal, and said torsion arms are fabricated from a single wafer of single crystal silicon. 
     
     
       8. The sense element of claim 3 wherein said planar semiconductive body, said pedestal, and said torsion arms are fabricated from a single wafer of single crystal silicon. 
     
     
       9. The sense element of claim 5 wherein said planar semiconductive body, said pedestal, and said torsion arms are fabricated from a single wafer of single crystal silicon. 
     
     
       10. The sense element of claim 6 wherein said planar semiconductive body, said pedestal, and said torsion arms are fabricated from a single wafer of single crystal silicon. 
     
     
       11. The sense element of claim 8 wherein said pedestal is anodically bonded to said substrate. 
     
     
       12. The sense element of claim 9 wherein said pedestal is anodically bonded to said substrate. 
     
     
       13. A torsion beam accelerometer sense element, comprising: a planar substrate;   a planar sensing member having at least a first internal opening;   mounting means positioned within said first internal opening for mounting said sensing member above said substrate, said mounting means comprising a pedestal having two opposed torsion arms defining a flexure axis about which said sensing member rotates responsive to acceleration normal to the plane of said substrate, said torsion arms fixed to said sensing member;   light side and heavy side plates of conductive material integral with said sensing member, said heavy side plate larger in area than said light side plate;   two pair of conductive plates defining heavy side and light side deflection capacitors, said heavy side deflection capacitor comprising said heavy side plate and a first conductive surface on said substrate below said heavy side plate, said light side deflection capacitor comprising said light side plate and a second conductive surface on said substrate below said light side plate, said light side and heavy side deflection capacitors arrayed substantially symmetrically on opposed sides of said flexure axis;   first and second slots in said heavy side plate extending proximately from said first internal opening and perpendicular to said flexure axis, inner longitudinal sides of said slots corresponding substantially to outer longitudinal edges of said conductive surface on said substrate below said heavy side plate, said slots extending a substantial portion of the length of said conductive surface on said substrate in the direction perpendicular to said flexure axis;   wherein said sensing member rotates about said flexure axis responsive to acceleration normal to the surface of said substrate, and wherein the capacitance of said heavy side and light side capacitors change in response to said rotation.   
     
     
       14. The sense element of claim 13 wherein said substrate is a dielectric substrate and said sensing member comprises a semiconductive body, wherein said first and second conductive surfaces on said substrate comprise metallized portions of rectilinear shape. 
     
     
       15. The sense of claim 13 wherein said slots extend to the outermost edge of said sensing member. 
     
     
       16. The sense of claim 14, wherein said slots extend to the outermost edge of said sensing member. 
     
     
       17. The sense element of claim 14 wherein said semiconductive body, said pedestal, and said torsion arms are fabricated from a single wafer of single crystal silicon. 
     
     
       18. The sense element of claim 17 wherein said dielectric substrate comprises glass, and wherein said pedestal is anodically bonded to said glass substrate. 
     
     
       19. The sense element of claim 13 wherein said sensing element further contains a plurality of through-holes sufficient to alter the damping coefficient of said sense element. 
     
     
       20. A torsion beam accelerometer sense element, comprising: a planar dielectric glass substrate;   a planar semiconductive sensing member having at least a first internal opening;   mounting means positioned within said first internal opening for mounting said sensing member above said substrate, said mounting means comprising a pedestal having two opposed torsion arms defining a flexure axis about which said sensing member rotates responsive to acceleration normal to the plane of said substrate, said torsion arms fixed to said sensing member;   light side and heavy side plates of conductive material integral with said sensing member, said heavy side plate larger in area than said light side plate;   two pair of conductive plates defining heavy side and light side deflection capacitors, said heavy side deflection capacitor comprising said heavy side plate and a conductive surface on said substrate below said heavy side plate, said light side deflection capacitor comprising said light side plate and a conductive surface on said substrate below said light side plate, said light side and heavy side deflection capacitors arrayed substantially symmetrically on opposed sides of said flexure axis;   first and second slots in said heavy side plate extending proximately from said internal opening and perpendicular to said flexure axis, inner longitudinal sides of said slots corresponding substantially to outer longitudinal edges of said conductive surface on said substrate below said heavy side plate, said slots extending a substantial portion of the length of said conductive surface on said substrate in the direction perpendicular to said flexure axis;   a pair of self-test conductive electrodes arrayed on either side of said conductive surface on said substrate below said heavy side plate, said self-test conductive electrodes together with said heavy side plate of said sensing member defining self-test capacitors causing said sensing member to rotate about said flexure axis when said heavy side plate and said self-test conductive electrodes do not have the same electrical potential;   wherein said sensing member rotates about said flexure axis responsive to acceleration normal to the surface of said substrate, and wherein the capacitance of said heavy side and light side capacitors change in response to said rotation.